Theories of the World from Antiquity to the Copernican Revolution: Second Revised Edition

Summary

This newly revised edition of Professor Crowe's accessible and enlightening book recreates one of the most dramatic developments in the history of thought: the change from an earth-centered to a sun-centered conception of the solar system. Written in a clear and straightforward manner, the work is organized around a hypothetical debate: Given the evidence available in 1615, which planetary system (Ptolemaic, Copernican, Tychonic, etc.) was most deserving of support?Beginning with an introductory chapter on celestial motions, Dr. Crowe proceeds to a discussion of Greek astronomy before Ptolemy, mathematical techniques used by ancient astronomers, the Ptolemaic system, the Copernican and Tychonic systems, and the contributions of Kepler and Galileo. In an epilogue, quotes from writers, philosophers, and scientists reveal the impact of Copernican thought on their work. Easily within the reach of anyone with a background in high school mathematics, this absorbing study offers a sound introduction to our solar system and an opportunity to relive one of the most momentous periods in intellectual history.

Theories of the World from Antiquity to the Copernican Revolution is an original work, first published by Dover Publications, Inc., in 1990. For this new edition, published in 2001, the author has made a number of additions and corrections.

Library of Congress Cataloging-in-Publication Data

Crowe, Michael J.

Theories of the world from antiquity to the Copernican Revolution / Michael J. Crowe.—2nd rev. ed.

p. cm.

Includes bibliographical references and index.

ISBN 0-486-41444-2 (pbk.)

1. Astronomy—History. I. Title.

QB15 .C77 2001

520’.9—dc21

00-046870

Manufactured in the United States by Courier Corporation

41444205

www.doverpublications.com

Preface

What This Book Is, and What It Is Not

One way to describe this book and its limitations is to offer, as was common among eighteenth-century authors, an extended title: A Selective History, Employing Elementary Geometrical Methods and Passages from the Writings of Ptolemy and Copernicus, of Theories of the Planetary System from Antiquity to 1615. A briefer if more ambiguous title would be: Given the Evidence in 1615, Which Theory of the Planetary System (the Ptolemaic, Copernican, Tychonic, etc.) Was Most Deserving of Support at That Time? As will be suggested subsequently, answers to this question have significant historical and philosophical implications.

A second way of characterizing the contents of this volume is to provide an account of its origin. Around 1976, after teaching these materials for fifteen years at the University of Notre Dame, I began to compile portions of them into class handouts. Within a decade they had grown into a book-length manuscript, prepared without any idea that it might eventually be published. A summer’s support from a National Endowment for the Humanities grant to Notre Dame for course development provided the opportunity to make a thorough revision of the materials and to put them into a word processor. The need for such materials arose from the fact that, although a number of excellent books cover this topic, none quite suited the needs of my students, who, although not yet ready for the technicalities treated in, say, Dreyer’s classic History of Astronomy from Thales to Kepler, were nonetheless willing to explore these materials in a way that does not neglect their mathematical character. Fortunately, the mathematical techniques essential for a sound understanding of the great astronomical debate surveyed in this book are within the reach of anyone with good high-school training in mathematics and a willingness to use it. It also seemed advantageous to include readings from Ptolemy and Copernicus, who were the central figures in this debate. And it has proved to be an engaging approach to organize the materials so as to prepare readers to debate whether, given the evidence in 1615, they would have opted for a geocentric or heliocentric universe. Every year since 1976, these materials have been tested in the classroom and subsequently revised and updated. Not long ago, a colleague, Professor André Goddu, who has also used these materials in his classes, suggested that they be offered to a publisher. The ideal choice seemed Dover, which press has for decades provided readers interested in the history of scientific thought with books distinguished both by high-quality contents and low price. Dover’s decision to publish it provided the opportunity for a final careful revision, designed to direct it to a larger public, while preserving those characteristics that have made it useful to the students the author has been privileged to teach.

This narrative of the origin of the book suggests to the reader that this volume is not a contribution to specialized research on the history of pre-1615 astronomy, for which many scholars possess superior credentials. It has rather been prepared to increase the accessibility of the writings of these scholars and of the great scientists whose writings they have so illuminated. The history provided is also selective, being organized chiefly around the aforementioned question.

Three Points of View

This book can be read more or less simultaneously from three different points of view: the scientific, the historical, and the philosophical.

If read for its scientific content, this book should provide a sound introductory knowledge of the astronomy of our solar system. The presentations of these ideas have been designed so as to draw, directly or indirectly, on the writings of a number of the most brilliant scientists of the past. Many of these ideas, being difficult, will challenge the reader’s abilities and ingenuity. Nonetheless, being fundamental for an understanding of the world, they are essential to a liberal education. It is an irony of current educational practice that whereas everyone believes the earth orbits the sun, few persons can cite the evidences that led to this conviction. Numerous presentations of the astronomy of the solar system are available; what makes the following presentation different from most of these are two features. On the one hand, the materials are presented historically (more on this shortly). On the other hand, the materials are set out so as to give primacy to an understanding of the scientific ideas involved. Each idea is carefully explained in such a way that only a minimum of background information is necessary for its comprehension. The use of a mathematical approach in presenting these ideas derives from the conviction that the most clear, direct, and effective way to an understanding of not only the scientific, but also the historical and philosophical features of the Copernican revolution, is through mathematics. This is not to say that mathematics alone is sufficient; it is only to suggest that Copernicus was correct when in the preface to his great work, he stressed that in a fundamental way, mathematics is necessary for an appreciation of his arguments. One irony of the study of the Copernican revolution as herein presented is that it is only by studying it from a mathematical point of view that one can fully understand the crucial historical point that mathematics alone was insufficient for both its creation and its resolution.

Second, the materials can also be read for their historical content. The Copernican revolution ranks as one of the most important developments in the entire history of thought. Moreover, the story of how humans came to create and then abandon the Ptolemaic system is among the most interesting and dramatic narratives in all of history. The reader should be aware that in the following materials, this story is not presented in its full richness; in particular, many individuals and events, important in their own right but not essential to the mainline of this drama, have not been included. To cite two examples, the impressive astronomical methods developed in antiquity by the Babylonians have been passed over with only the briefest mention, and the significant advances in astronomy during the medieval period have also received less attention than would be expected in a study claiming comprehensiveness. The main justification for such omissions is that the materials have been selected so as to provide a knowledge of developments involved in a single grand-scale episode in the history of astronomy: the Copernican revolution. The goal behind this method of proceeding is to involve the reader as fully and directly as possible in this single episode, to provide an understanding of the ideas and problems of the individuals who played the most crucial roles in that episode.

One advantage of a historical approach is suggested by a passage from the writings of the German historian and philosopher Wilhelm Dilthey (1833–1911). In discussing the uses of history, Dilthey presented an idea that, although phrased in terms of religious history, applies with equal force to the history of scientific thought. He suggested that acquisition of historical experience can offset an unfortunate feature of our lives—that as we grow older, the range of our experiences becomes ever more limited. Nonetheless, Dilthey stated,

. . . when I run through Luther’s letters and writings, the reports of his contemporaries, the records of the religious conferences and councils as well as of his official communications, I live through a religious process of such eruptive power, of such energy, in which it is a matter of life or death, that it lies beyond any possibility of personal experience for a man of our day. But I can relive it.¹

In short, these materials are designed to offer the reader an opportunity to relive to some extent one of the most dramatic developments in the history of thought. The chance of achieving this result will be enhanced by a commitment to understanding the ideas and arguments formulated by the pioneering astronomers and discussed in this book. The decision to adopt this approach has suggested some practices that may seem strange to twentieth-century readers. For example, what are now called the Keplerian Laws of Motion are herein referred to as the Keplerian Conjectures, which more adequately characterizes how most of Kepler’s contemporaries, at least those who took any notice of them, conceived them. To put this approach in different terms, we shall be examining both one product of science (the theory that the earth orbits the sun), and also the process by which that theory was attained. This approach, in which both the product and process of science are examined, can provide a fresh and more humanized view of science. We shall encounter not only scientific creations, but also scientific creators, not only settled conclusions, but also intense controversies. The restriction of the scientific ideas in this book to those available in 1615 has not precluded presentation of historical information that has become available since that year. An example of this is the Appendix to the book, which consists of a presentation of very recent theories of the astronomical functions of such megalithic sites as Stonehenge, even though no historian alive in 1615 possessed a knowledge of these theories. Readers uninterested in these theories can omit this presentation without losing anything other than some illustrations of the information contained in Chapter One.

Third, this book presents various philosophical ideas and issues. The Copernican claim that the sun, not the earth, is the center of our system presented many challenges to traditional philosophical and theological beliefs. A number of these challenges are discussed in the book and illustrated in its Epilogue, which consists of a collection of quotations from various authors who pondered these issues with special intensity. Moreover, the Copernican revolution raises an array of methodological issues, such as the nature of scientific discovery and verification, the status of theoretical entities, and the role of empirical evidence. The two methodological questions that emerge most strikingly from these materials are (1) what is the relation of scientific theories to empirical information, and (2) what approach should be taken concerning the nature and testing of scientific theories? Francis Bacon is among those who have urged in regard to the first issue that scientific theories arise from empirical information; in fact, his writings seem at times to convey the claim that the necessary and sufficient basis for the creation of new scientific theories is detailed knowledge of the phenomena. Other philosophers have challenged this view, which is frequently termed inductivism, urging that empirical factors are usually insufficient for either the creation or adequate testing of scientific theories. A crucial question involved in the second issue is whether theories should be viewed as primarily instruments, as useful fictions devised to account for the world and to predict future events, or whether they should be construed in a realist sense, as hopefully true portrayals of nature that can be expected not only to account for and to predict debate whether, given the evidence in 1615, they would have opted for a geocentric or heliocentric universe. Every year since 1976, these materials have been tested in the classroom and subsequently revised and updated. Not long ago, a colleague, Professor André Goddu, who has also used these materials in his classes, suggested that they be offered to a publisher. The ideal choice seemed Dover, which press has for decades provided readers interested in the history of scientific thought with books distinguished both by high-quality contents and low price. Dover’s decision to publish it provided the opportunity for a final careful revision, designed to direct it to a larger public, while preserving those characteristics that have made it useful to the students the author has been privileged to teach.

This narrative of the origin of the book suggests to the reader that this volume is not a contribution to specialized research on the history of pre-1615 astronomy, for which many scholars possess superior credentials. It has rather been prepared to increase the accessibility of the writings of these scholars and of the great scientists whose writings they have so illuminated. The history provided is also selective, being organized chiefly around the aforementioned question.

Three Points of View

This book can be read more or less simultaneously from three different points of view: the scientific, the historical, and the philosophical.

If read for its scientific content, this book should provide a sound introductory knowledge of the astronomy of our solar system. The presentations of these ideas have been designed so as to draw, directly or indirectly, on the writings of a number of the most brilliant scientists of the past. Many of these ideas, being difficult, will challenge the reader’s abilities and ingenuity. Nonetheless, being fundamental for an understanding of the world, they are essential to a liberal education. It is an irony of current educational practice that whereas everyone believes the earth orbits the sun, few persons can cite the evidences that led to this conviction. Numerous presentations of the astronomy of the solar system are available; what makes the following presentation different from most of these are two features. On the one hand, the materials are presented historically (more on this shortly). On the other hand, the materials are set out so as to give primacy to an understanding of the scientific ideas involved. Each idea is carefully explained in such a way that only a minimum of background information is necessary for its comprehension. The use of a mathematical approach in presenting these ideas derives from the conviction that the most clear, direct, and effective way to an understanding of not only the scientific, but also the historical and philosophical features of the Copernican revolution, is through mathematics. This is not to say that mathematics alone is sufficient; it is only to suggest that Copernicus was correct when in the preface to his great work, he stressed that in a fundamental way, mathematics is necessary for an appreciation of his arguments. One irony of the study of the Copernican revolution as herein presented is that it is only by studying it from a mathematical point of view that one can fully understand the crucial historical point that mathematics alone was insufficient for both its creation and its resolution.

Second, the materials can also be read for their historical content. The Copernican revolution ranks as one of the most important developments in the entire history of thought. Moreover, the story of how humans came to create and then abandon the Ptolemaic system is among the most interesting and dramatic narratives in all of history. The reader should be aware that in the following materials, this story is not presented in its full richness; in particular, many individuals and events, important in their own right but not essential to the mainline of this drama, have not been included. To cite two examples, the impressive astronomical methods developed in antiquity by the Babylonians have been passed over with only the briefest mention, and the significant advances in astronomy during the medieval period have also received less attention than would be expected in a study claiming comprehensiveness. The main justification for such omissions is that the materials have been selected so as to provide a knowledge of developments involved in a single grand-scale episode in the history of astronomy: the Copernican revolution. The goal behind this method of proceeding is to involve the reader as fully and directly as possible in this single episode, to provide an understanding of the ideas and problems of the individuals who played the most crucial roles in that episode.

One advantage of a historical approach is suggested by a passage from the writings of the German historian and philosopher Wilhelm Dilthey (1833–1911). In discussing the uses of history, Dilthey presented an idea that, although phrased in terms of religious history, applies with equal force to the history of scientific thought. He suggested that acquisition of historical experience can offset an unfortunate feature of our lives—that as we grow older, the range of our experiences becomes ever more limited. Nonetheless, Dilthey stated,

. . . when I run through Luther’s letters and writings, the reports of his contemporaries, the records of the religious conferences and councils as well as of his official communications, I live through a religious process of such eruptive power, of such energy, in which it is a matter of life or death, that it lies beyond any possibility of personal experience for a man of our day. But I can relive it.²

In short, these materials are designed to offer the reader an opportunity to relive to some extent one of the most dramatic developments in the history of thought. The chance of achieving this result will be enhanced by a commitment to understanding the ideas and arguments formulated by the pioneering astronomers and discussed in this book. The decision to adopt this approach has suggested some practices that may seem strange to twentieth-century readers. For example, what are now called the Keplerian Laws of Motion are herein referred to as the Keplerian Conjectures, which more adequately characterizes how most of Kepler’s contemporaries, at least those who took any notice of them, conceived them. To put this approach in different terms, we shall be examining both one product of science (the theory that the earth orbits the sun), and also the process by which that theory was attained. This approach, in which both the product and process of science are examined, can provide a fresh and more humanized view of science. We shall encounter not only scientific creations, but also scientific creators, not only settled conclusions, but also intense controversies. The restriction of the scientific ideas in this book to those available in 1615 has not precluded presentation of historical information that has become available since that year. An example of this is the Appendix to the book, which consists of a presentation of very recent theories of the astronomical functions of such megalithic sites as Stonehenge, even though no historian alive in 1615 possessed a knowledge of these theories. Readers uninterested in these theories can omit this presentation without losing anything other than some illustrations of the information contained in Chapter One.

Third, this book presents various philosophical ideas and issues. The Copernican claim that the sun, not the earth, is the center of our system presented many challenges to traditional philosophical and theological beliefs. A number of these challenges are discussed in the book and illustrated in its Epilogue, which consists of a collection of quotations from various authors who pondered these issues with special intensity. Moreover, the Copernican revolution raises an array of methodological issues, such as the nature of scientific discovery and verification, the status of theoretical entities, and the role of empirical evidence. The two methodological questions that emerge most strikingly from these materials are (1) what is the relation of scientific theories to empirical information, and (2) what approach should be taken concerning the nature and testing of scientific theories? Francis Bacon is among those who have urged in regard to the first issue that scientific theories arise from empirical information; in fact, his writings seem at times to convey the claim that the necessary and sufficient basis for the creation of new scientific theories is detailed knowledge of the phenomena. Other philosophers have challenged this view, which is frequently termed inductivism, urging that empirical factors are usually insufficient for either the creation or adequate testing of scientific theories. A crucial question involved in the second issue is whether theories should be viewed as primarily instruments, as useful fictions devised to account for the world and to predict future events, or whether they should be construed in a realist sense, as hopefully true portrayals of nature that can be expected not only to account for and to predict natural phenomena, but also to explain them. These issues are fundamental for far more than astronomy; they are, in fact, relevant to almost every area of learning.

Acknowledgments

I am, first of all, deeply indebted to the many students at the University of Notre Dame who have not only inspired the preparation of these materials, but also by their questions and comments have increased their clarity and accessibility. Special thanks are due to one of the most recent of these, Jamie Brummer, who located many of the literary statements concerning the Copernican revolution